U.S. patent application number 12/646224 was filed with the patent office on 2010-07-08 for aircraft air-conditioning system with a reduced risk of icing.
This patent application is currently assigned to AIRBUS OPERATIONS GMBH. Invention is credited to Joerg Baumann, Dariusz Krakowski, Michael Markwart, Martin Schmid.
Application Number | 20100173576 12/646224 |
Document ID | / |
Family ID | 42243524 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100173576 |
Kind Code |
A1 |
Schmid; Martin ; et
al. |
July 8, 2010 |
Aircraft Air-Conditioning System With A Reduced Risk Of Icing
Abstract
An aircraft air-conditioning system (10) comprises an
air-conditioning unit (12) that is connected by a main fresh-air
line (16) to a mixer (18) in order to supply the mixer (18) with
fresh air at a desired low temperature. A fresh-air branch line
(20) that is connected upstream of the mixer (18) to the main
fresh-air line (16) has a flow cross section that is smaller than a
flow cross section of the main fresh-air line (16). In a region of
connection of the main fresh-air line (16) to the fresh-air branch
line (20) the main fresh-air line (16) and the fresh-air branch
line (20) are so formed that a main fresh air flow flowing through
the main fresh-air line (16) is deflected, while a fresh air branch
flow flowing through the fresh-air branch line (20) experiences
substantially no deflection,
Inventors: |
Schmid; Martin; (Hamburg,
DE) ; Krakowski; Dariusz; (Buxtehude, DE) ;
Markwart; Michael; (Halstenbek, DE) ; Baumann;
Joerg; (Hamburg, DE) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP
2700 CAREW TOWER, 441 VINE STREET
CINCINNATI
OH
45202
US
|
Assignee: |
AIRBUS OPERATIONS GMBH
Hamburg
DE
|
Family ID: |
42243524 |
Appl. No.: |
12/646224 |
Filed: |
December 23, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61142420 |
Jan 5, 2009 |
|
|
|
Current U.S.
Class: |
454/75 ;
454/76 |
Current CPC
Class: |
B64D 13/08 20130101;
Y02T 50/56 20130101; Y02T 50/50 20130101; B64D 2013/0666
20130101 |
Class at
Publication: |
454/75 ;
454/76 |
International
Class: |
B60H 1/00 20060101
B60H001/00; B64D 13/08 20060101 B64D013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2009 |
DE |
102009003937.6 |
Claims
1. Aircraft air-conditioning system (10), comprising: an
air-conditioning unit (12) that is connected by a main fresh-air
line (16) to a mixer (18) in order to supply the mixer (18) with
fresh air at a desired low temperature, and a fresh-air branch line
(20) that is connected upstream of the mixer (18) to the main
fresh-air line (16), wherein the fresh-air branch line (20) has a
flow cross section that is smaller than a flow cross section of the
main fresh-air line (16), characterized in that the main fresh-air
line (16) and the fresh-air branch line (20) in a region of
connection of the main fresh-air line (16) to the fresh-air branch
line (20) is are so formed that a main fresh air flow flowing
through the main fresh-air line (16) is deflected, while a fresh
air branch flow flowing through the fresh-air branch line (20)
experiences substantially no deflection.
2. Aircraft air-conditioning system according to claim 1,
characterized in that the main fresh-air line (16) in the region of
connection of the main fresh-air line (16) to the fresh-air branch
line (20) branches into a first main fresh-air line branch (32) and
a second main fresh-air line branch (34), wherein the first main
fresh-air line branch (32) and the second main fresh-air line
branch (34) each have a flow cross section that is larger than the
flow cross section of the fresh-air branch line (20).
3. Aircraft air-conditioning system according to claim 1,
characterized by a heating device (28), which is adapted to heat
the main fresh-air line (16) and/or the fresh-air branch line (20)
in the region of connection of the main fresh-air line (16) to the
fresh-air branch line (20).
4. Aircraft air-conditioning system according to claim 3,
characterized by a control unit (22), which is adapted to control
the heating device (28) in dependence on at least one measured
parameter that indicates icing of the region of connection of the
main fresh-air line (16) to the fresh-air branch line (20), wherein
the measured parameter is a parameter that is characteristic of the
static pressure in the main fresh-air line (16), a parameter that
is characteristic of the static pressure in the fresh-air branch
line (20) and/or a parameter that is characteristic of the
temperature in a region of the aircraft that is connected to the
main fresh-air line (16) and/or the fresh-air branch line (20)
downstream of the region of connection of the main fresh-air line
(16) to the fresh-air branch line (20).
5. Aircraft air-conditioning system according to claim 3,
characterized in that the heating device (28) is adapted to heat
the region of connection of the main fresh-air line (16) to the
fresh-air branch line (20) in a purposeful and locally selective
manner.
6. Aircraft air-conditioning system according to claim 3,
characterized in that the heating device (28) comprises a line,
through which a heat transfer fluid may flow, and that the
fresh-air branch line (20) in the region of connection of the main
fresh-air line (16) to the fresh-air branch line (20) extends
through the line, through which a heat transfer fluid may flow.
7. Aircraft air-conditioning system according to claim 6,
characterized in that the line, through which a heat transfer fluid
may flow, is a recirculated-air line (30) for recirculating
filtered air from a passenger cabin of the aircraft.
8. Aircraft air-conditioning system according to claim 6,
characterized in that the line, through which a heat transfer fluid
may flow, opens out into the main fresh-air line (16) in the region
of connection of the main fresh-air line (16) to the fresh-air
branch line (20).
9. Aircraft air-conditioning system according to claim 1,
characterized in that the fresh-air branch line (20) is uninsulated
in the region of connection of the main fresh-air line (16) to the
fresh-air branch line (20).
10. Aircraft air-conditioning system according to claim 1,
characterized by a control unit (22), which is adapted to control
the operation of the air-conditioning unit (12) and/or the supply
of warm air into the main fresh-air line (16) downstream of the
air-conditioning unit (12) and upstream of the region of connection
of the main fresh-air line (16) to the fresh-air branch line (20)
in such a way that the temperature of the air flowing through the
region of connection of the main fresh-air line (16) to the
fresh-air branch line (20) does not fall below a first
predetermined temperature value (T.sub.1).
11. Aircraft air-conditioning system according to claim 10,
characterized in that the first predetermined temperature value
(T.sub.1) is in the range between 0.degree. C. and 5.degree. C.
12. Aircraft air-conditioning system according to claim 1,
characterized by a control unit (22), which is adapted to control
the operation of the air-conditioning unit (12) and/or the supply
of warm air into the main fresh-air line (16) downstream of the
air-conditioning unit (12) and upstream of the region of connection
of the main fresh-air line (16) to the fresh-air branch line (20)
in such a way that the temperature of the air flowing through the
region of connection of the main fresh-air line (16) to the
fresh-air branch line (20) does not exceed a second predetermined
temperature value (T.sub.2).
13. Aircraft air-conditioning system according to claim 12,
characterized in that the second predetermined temperature value
(T.sub.2) is in the range between -15.degree. C. and -10.degree. C.
Description
[0001] The present invention relates to an aircraft
air-conditioning system with a reduced risk of icing in a region of
connection of a main fresh-air line to a fresh-air branch line.
[0002] In a modern passenger aircraft the passenger cabin or
sub-regions of the passenger cabin, the hold or sub-regions of the
hold, the cockpit and the crew restrooms form various
air-conditioning zones that are conventionally air-conditioned both
during cruising and during operation of the aircraft on the ground
by means of an onboard air-conditioning system. The aircraft
air-conditioning system is supplied with hot bleed air under
increased pressure that is removed from the engine compressors or
auxiliary engine compressors. In the air-conditioning units, the
so-called air-conditioning packs of the aircraft air-conditioning
system, the bleed air is expanded is and cooled to a desired low
temperature. Finally, the air conditioned in the air-conditioning
units is directed as cooled fresh air into a main fresh-air line of
the air-conditioning system. The fresh air flowing through the main
fresh-air line is conveyed into a mixer, where it is mixed with
recirculated air extracted from the passenger cabin. The mixed air
produced in the mixer from cold fresh air provided by the
air-conditioning packs and from recirculated air extracted from the
aircraft cabin is finally used to air-condition the various
air-conditioning zones of the aircraft.
[0003] In order to allow individual air-conditioning zones of the
aircraft, for example a hold region or the cockpit, to be
air-conditioned individually independently of recirculated air,
fresh air has to be removed upstream of the mixer from the main
fresh-air line of the aircraft air-conditioning system.
Conventionally, a fresh-air branch line that branches off upstream
of the mixer from the main fresh-air line is used for this purpose.
In a fresh-air branch line branching off from the main fresh-air
line, however, regions where a fresh air branch flow directed
through the fresh-air branch line has a reduced flow rate usually
occur. As a result, in the event of a corresponding temperature and
a corresponding moisture content of the fresh air, the attachment
of ice and snow to the lines of the air-conditioning system is
promoted in the region where the fresh-air branch line branches off
from the main fresh-air line. The smaller the cross section of flow
of the fresh-air branch line, the greater the risk of icing in the
region where the fresh-air branch line branches off from the main
fresh-air line.
[0004] From DE 10 2006 037 539 A1 it is known for fresh-air lines,
through which cold fresh air from the air-conditioning units of an
aircraft air-conditioning system flows, to be protected against
icing by means of a supply of warm engine bleed air that is
controlled by trimming valves. However, as a result of the supply
of warm engine bleed air into the fresh-air lines the cooling
capacity of the air-conditioning system is reduced. Furthermore,
the trimming valves needed to control the supply of engine bleed
air into the fresh-air lines are relatively susceptible to faults.
This leads to an increased outlay for maintenance as a failure of
the trimming valves would result in impairment of the operation of
the aircraft.
[0005] The invention is directed to the object of indicating an
aircraft air-conditioning system with a reduced risk of icing in a
region of connection of a main fresh-air line to a fresh-air branch
line.
[0006] In order to achieve this object, an aircraft
air-conditioning system according to the invention comprises an
air-conditioning unit that is connected by a main fresh-air line to
a mixer in order to supply the mixer with fresh air at a desired
low temperature. A fresh-air branch line having a flow cross
section that is smaller than a flow cross section of the main
fresh-air line is connected upstream of the mixer to the main
fresh-air line. In a region of connection of the main fresh-air
line to the fresh-air branch line the main fresh-air line and the
fresh-air branch line are so formed that a main fresh air flow
flowing through the main fresh-air line is deflected, while a fresh
air branch flow flowing through the fresh-air branch line
experiences substantially no deflection. In other words, the
fresh-air branch line extends substantially in the direction of the
main fresh air flow through the main fresh-air line upstream of the
region of connection of the main fresh-air line to the fresh-air
branch line, while the main fresh-air line is of a curved design
relative to the flow direction of the main fresh air flow through
the main fresh-air line upstream of the region of connection of the
main fresh-air line to the fresh-air branch line.
[0007] By virtue of the development according to the invention of
the main fresh-air line and the fresh-air branch line in the region
of connection of the main fresh-air line to the fresh-air branch
line, the effect that arises in prior art aircraft air-conditioning
systems, namely that in a fresh-air branch line branching off from
a main fresh-air line regions where a fresh air branch flow
directed through the fresh-air branch line has a reduced flow rate
occur, is avoided or at least sharply reduced. This lowers the risk
of ice and/or snow attaching in the interior of the fresh-air
branch line. As the main fresh-air line compared to the fresh-air
branch line has a larger flow cross section, in the main fresh-air
line the risk of icing is markedly lower than in the fresh-air
branch line. Regions that have a reduced flow rate of the main
fresh air flow directed through the main fresh-air line and occur
as a result of the deflection of the main fresh air flow in the
region of connection of the main fresh-air line to the fresh-air
branch line therefore have a much lower influence upon the risk of
icing than the occurrence of such regions with a reduced flow rate
in the fresh-air branch line. The--in terms of flow--advantageous
design of the region of connection of the main fresh-air line to
the fresh-air branch line therefore makes it possible markedly to
reduce the risk of icing in the region of connection of the main
fresh-air line to the fresh-air branch line.
[0008] The main fresh-air line of the aircraft air-conditioning
system according to the invention may comprise merely a line
branch. The region of connection of the main fresh-air line to the
fresh-air branch line may then, as already described, be designed
in such a way that the fresh-air branch line extends in a direction
that corresponds substantially to the direction of the main fresh
air flow through the main fresh-air line upstream of the region of
connection of the main fresh-air line to the fresh-air branch line.
The main fresh-air line, on the other hand, follows a curve in the
region of connection of the main fresh-air line to the fresh-air
branch line.
[0009] It is however also possible for the main fresh-air line in
the region of connection of the main fresh-air line to the
fresh-air branch line to branch into a first main fresh-air line
branch and a second main fresh-air line branch. The first main
fresh-air line branch and the second main fresh-air line branch are
then preferably so formed that the main fresh air branch flows
flowing through the main fresh-air line branches are deflected in
the region of connection of the main fresh-air line to the
fresh-air branch line. In contrast thereto, the fresh air branch
flow flowing through the fresh-air branch line experiences no
deflection, i.e. the direction of the fresh air branch flow in the
fresh-air branch line corresponds substantially to the direction of
the main fresh air flow through the main fresh-air line upstream of
the region of connection of the main fresh-air line to the
fresh-air branch line. In order once again to guarantee the desired
reduction of the risk of icing in the region of connection of the
main fresh-air line to the fresh-air branch line, the first main
fresh-air line branch and the second main fresh-air line branch
each have a flow cross section that is greater than the flow cross
section of the fresh-air branch line.
[0010] The aircraft air-conditioning system according to the
invention preferably further comprises a heating device, which is
adapted to heat the main fresh-air line and/or the fresh-air branch
line in the region of connection of the main fresh-air line to the
fresh-air branch line. By virtue of the provision of a heating
device it may be ensured that, even in operating phases of the
aircraft air-conditioning system when for example the aircraft
air-conditioning system is being operated under critical ambient
conditions or in a critical temperature range, icing in the region
of connection of the main fresh-air line to the fresh-air branch
line may be reliably avoided.
[0011] The aircraft air-conditioning system according to the
invention may further comprise a control unit, which is adapted to
control the heating device in dependence on at least one measured
parameter that indicates icing of the region of connection of the
main fresh-air line to the fresh-air branch line. For this purpose,
the control unit may be connected to appropriate sensors. The
measured parameter may be a parameter that is characteristic of the
static pressure in the main fresh-air line and/or of the static
pressure in the fresh-air branch line. Measuring of the static
pressure may be used to detect icing of the region of connection of
the main fresh-air line to the fresh-air branch line as the
attachment of ice and/or snow in the main fresh-air line and/or the
fresh-air branch line immediately leads to a rise of the static
pressure upstream of the relevant pipe section.
[0012] Alternatively or in addition thereto, the control unit may
be adapted to use the temperature in a region of the aircraft that
is connected to the main fresh-air line and/or the fresh-air branch
line downstream of the region of connection of the main fresh-air
line to the fresh-air branch line as a parameter for detecting
icing of the region of connection of the main fresh-air line to the
fresh-air branch line. For example, in the critical temperature
range of -10.degree. C. to 0.degree. C. the constant temperature of
a temperature sensor at 0.degree. C. may be an indication of icing
on the sensor and in the pipe.
[0013] Preferably, the control unit starts operation of the heating
device if at least one measured value of a parameter, which is
being monitored by the control unit to detect icing of the region
of connection of the main fresh-air line to the fresh-air branch
line, exceeds a predetermined threshold value. If the measured
value of the parameter being monitored to detect icing of the
region of connection of the main fresh-air line to the fresh-air
branch line drops back down below the threshold value, the control
unit may terminate operation of the heating unit. Alternatively or
in addition thereto, the control unit may provide a periodic
operation of the heating device, i.e. start the heating device
after a specific time interval without heating has elapsed and then
switch off the heating device after a heating period has
elapsed.
[0014] The heating device may comprise an engine bleed-air line,
which downstream of the air-conditioning unit and upstream of the
region of connection of the main fresh-air line to the fresh-air
branch line is connected to the main fresh-air line in order to
supply warm engine bleed air to the main fresh-air line. Control of
the supply of warm engine bleed air from the engine bleed-air line
into the main fresh-air line may so be effected by means of a valve
disposed in the engine bleed-air line. Heating the region of
connection of the main fresh-air line to the fresh-air branch line
by supplying warm engine bleed air into the main fresh-air line
makes it possible reliably to avoid and/or eliminate icing of the
region of connection of the main fresh-air line to the fresh-air
branch line. During the heating periods the aircraft
air-conditioning is system however delivers a reduced cooling
capacity, which may lead to a deterioration of comfort for the
passengers and crew on board the aircraft. Furthermore, during the
heating periods ice that has attached in the region of connection
of the main fresh-air line to the fresh-air branch line may detach
itself and damage downstream components of the air-conditioning
system and/or even be carried into the passenger cabin. The time
interval between the heating periods should be kept as short as
possible to prevent the formation and detachment of larger
fragments.
[0015] As an alternative or in addition to a heating device
comprising an engine bleed-air line, the aircraft air-conditioning
system according to the invention preferably comprises a heating
device that enables purposeful and locally selective heating of the
region of connection of the main fresh-air line to the fresh-air
branch line. In other words, the heating device is preferably
designed in such a way that it allows a purposeful supply of
thermal energy to the, in terms of the risk of icing, critical
region of connection of the main fresh-air line to the fresh-air
branch line. For example, the heating device may be an electric
heating device, which for releasing thermal energy to the region of
connection of the main fresh-air line to the fresh-air branch line
is disposed adjacent to the region of connection of the main
fresh-air line to the fresh-air branch line,
[0016] Alternatively or in addition thereto, the heating device for
purposeful and locally selective heating of the region of
connection of the main fresh-air line to the fresh-air branch line
may comprise a line, through which a heat transfer fluid may flow.
The fresh-air branch line may then in the region of connection of
the main fresh-air line to the fresh-air branch line extend through
the line, through which a heat transfer fluid may flow, thereby
enabling an unimpeded heat transfer from the line, through which a
heat transfer fluid may flow, to the fresh-air branch line. A
heating device comprising a line, through which a heat transfer
fluid may flow, may be controlled by controlling the supply of heat
transfer fluid into the line, for example by means of a suitable
valve. The line, through which a heat transfer fluid may flow, may
be for example an engine bleed-air line or a line that removes
waste heat from a heat-generating component on board the
aircraft.
[0017] The line, through which a heat transfer fluid may flow, is
however preferably a recirculated-air line for recirculating
filtered cabin air of the aircraft. The use of waste heat of a
heat-generating component on board the aircraft or the use of the
thermal energy contained in the recirculated air removed from the
passenger cabin of the aircraft to heat the region of connection of
the main fresh-air line to the fresh-air branch line is
particularly energy-efficient as it is possible to dispense with
the provision of an additional energy source, such as is needed for
example to operate an electric heating device.
[0018] The line, through which a heat transfer fluid may flow, may
open out into the main fresh-air line in the region of connection
of the main fresh-air line to the fresh-air branch line. Given such
an arrangement, a mixture of fresh air and heat transfer fluid
flows through the main fresh-air line downstream of the region of
connection of the main fresh-air line to the fresh-air branch line.
This is particularly unproblematic if the line, through which a
heat transfer fluid may flow, is a recirculated-air line for
recirculating filtered cabin air of the aircraft.
[0019] In the region of connection of the main fresh-air line to
the fresh-air branch line the fresh-air branch line may be
uninsulated, i.e. not provided with an insulating sheath.
[0020] This guarantees an optimized input of the heat generated by
a heating device into the region of connection of the main
fresh-air line to the fresh-air branch line. Heating of the
fresh-air branch line is particularly efficient if it is
manufactured from a heat-conducting material, such as for example
metal.
[0021] The aircraft air-conditioning system according to the
invention may further comprise a control unit, which is adapted to
control the operation of the air-conditioning unit and/or the
supply of warm air into the main fresh-air line downstream of the
air-conditioning unit and upstream of the region of connection of
the main fresh-air line to the fresh-air branch line in such a way
that the temperature of the air flowing through the region of
connection of the main fresh-air line to the fresh-air branch line
does not fall below a first predetermined temperature value.
[0022] The first predetermined temperature value is preferably in
the range between 0.degree. C. and 5.degree. C. By controlling the
temperature of the air flowing through the region of connection of
the main fresh-air line to the fresh-air branch line in such a way
that this temperature does not fall below 0.degree. C. to 5.degree.
C., icing of the region of connection of the main fresh-air line to
the fresh-air branch line is reliably prevented. Such temperature
control however usually requires a higher volume rate of fresh air
flow to provide a desired cooling capacity of the aircraft
air-conditioning system. Furthermore, occasionally the cooling
capacity of the aircraft air-conditioning system may not be
sufficient to avoid an impairment of comfort for the passengers and
crew on board the aircraft. If possible, therefore, the temperature
of the air flowing through the region of connection of the main
fresh-air line to the fresh-air branch line should be controlled to
prevent it falling below 0.degree. C. to 5.degree. C. only in
operating phases of the aircraft air-conditioning system that are
particularly critical with regard to a risk of icing of the region
of connection of the main fresh-air line to the fresh-air branch
line.
[0023] The aircraft air-conditioning system according to the
invention may further comprise a control unit, which is adapted to
control the operation of the air-conditioning unit and/or the
supply of warm air into the main fresh-air line downstream of the
air-conditioning unit and upstream of the region of connection of
the main fresh-air line to the fresh-air branch line in such a way
that the temperature of the air flowing through the region of
connection of the main fresh-air line to the fresh-air branch line
does not exceed a second predetermined temperature value. The
aircraft air-conditioning system according to the invention
preferably comprises a control unit, which is devised, depending
upon requirements, to control the temperature of the air flowing
through the region of connection of the main fresh-air line to the
fresh-air branch line in such a way that the temperature neither
falls below the first predetermined temperature value nor exceeds
the second predetermined temperature value.
[0024] The second predetermined temperature value is preferably in
the range between -15.degree. C. and -10.degree. C. If the aircraft
air-conditioning system is operated in such a way that the
temperature of the air flowing through the region of connection of
the main fresh-air line to the fresh-air branch line lies between
-15.degree. C. and -10.degree. C., the air-conditioning unit is
capable of removing 75% of the moisture, which is contained in the
air supplied to the air-conditioning system, from the air. The
fresh air flowing through the region of connection of the main
fresh-air line to the fresh-air branch line then consequently has a
relatively low moisture content, thereby reducing the risk of icing
in this region. If the temperature of the air flowing through the
region of connection of the main fresh-air line to the fresh-air
branch line is controlled in such a way that it does not exceed a
value of -15.degree. C. to -10.degree. C., a relatively large
quantity of warm engine bleed air has to be supplied to the fresh
air downstream of the region of connection of the main fresh-air
line to the fresh-air branch line in order to avoid an impairment
of comfort for the passengers and crew on board the aircraft.
Supply of the warm engine bleed air is effected with the aid of
valves that are possibly susceptible to faults. For these reasons,
the temperature of the air flowing through the region of connection
of the main fresh-air line to the fresh-air branch line should be
controlled to prevent it exceeding -15.degree. C. to -10.degree. C.
as far as possible only in operating phases of the aircraft
air-conditioning system, which are critical with regard to a risk
of icing of the region of connection of the main fresh-air line to
the fresh-air branch line and in which high cooling capacity
requirements are demanded of the air-conditioning system.
[0025] Preferred embodiments of the invention are now described in
detail with reference to the accompanying diagrammatic drawings,
which show in
[0026] FIG. 1 a detail of a first embodiment of an aircraft
air-conditioning system,
[0027] FIG. 2 a detail of a second embodiment of an aircraft
air-conditioning system and
[0028] FIG. 3 a detail view of a region of connection of a main
fresh-air line to a fresh-air branch line in an aircraft
air-conditioning system.
[0029] FIG. 1 shows a detail of an aircraft air-conditioning system
10 comprising an air-conditioning unit 12, to which hot bleed air
under increased pressure is supplied through a first engine
bleed-air line 14. In the air-conditioning unit 12 the bleed air is
expanded and cooled to a desired low temperature. The air
conditioned in the air-conditioning unit 12 is finally directed
through a main fresh-air line 16 into a mixer 18, where it is mixed
with recirculated air extracted from a passenger cabin of the
aircraft. The mixed air produced in the mixer 18 from cold fresh
air supplied by the air-conditioning unit 12 and from recirculated
air extracted from the aircraft cabin is finally used to
air-condition various air-conditioning zones, in particular the
passenger cabin of the aircraft.
[0030] Individual air-conditioning zones of the aircraft, for
example individual hold regions or the cockpit should however be
supplied with fresh air independently of recirculated air. For this
purpose a fresh-air branch line 20 is provided, which is connected
to the main fresh-air line 16 upstream of the mixer 18, i.e,
upstream of a region, in which the fresh air flowing through the
main fresh-air line 16 is mixed with recirculated air. Because of
the relatively low fresh air requirement of the aircraft is regions
to be supplied with fresh air by the fresh-air branch line 20, the
fresh-air branch line 20 has a flow cross section that is smaller
than a flow cross section of the main fresh-air line 16.
[0031] In a region of connection of the main fresh-air line 16 to
the fresh-air branch line 20 the main fresh-air line 16 is of a
curved design so that a main fresh air flow flowing through the
main fresh-air line 16 is deflected. In contrast thereto, the
fresh-air branch line 20 in the region of connection of the main
fresh-air line 16 to the fresh-air branch line 20 extends in a
direction that corresponds to the flow direction of the fresh air
through the main fresh-air line 16 upstream of the region of
connection of the main fresh-air line 16 to the fresh-air branch
line 20, so that a fresh air branch flow flowing through the
fresh-air branch line 20 experiences substantially no
deflection.
[0032] This development of the region of connection of the main
fresh-air line 16 to the fresh-air branch line 20 prevents the
occurrence of regions in the fresh-air branch line 20 where the
fresh air branch flow directed through the fresh-air branch line 20
has a reduced flow rate. It is thereby possible markedly to reduce
the risk of the attachment of ice and/or snow in the fresh-air
branch line 20 in the event of a corresponding temperature and a
corresponding moisture content of the fresh air flowing through the
region of connection of the main fresh-air line 16 to the fresh-air
branch line 20. Admittedly, in the curved main fresh-air line 16
the occurrence of regions where the main fresh air flow flowing
through the main fresh-air line 16 has a reduced flow rate is not
ruled out. However, the--compared to the flow cross section of the
fresh-air branch line 20--markedly larger flow cross section of the
main fresh-air line 16 lowers the risk of ice and/or snow attaching
in the main fresh-air line 16 in the region of connection of the
main fresh-air line 16 to the fresh-air branch line 20.
[0033] The aircraft air-conditioning system 10 further comprises an
electronic control unit 22 that is adapted to perform various
control functions during operation of the air-conditioning system
10. For example, the electronic control unit 22 may control a valve
26 disposed in a second engine bleed-air line 24. The second engine
bleed-air line 24 opens out into the main fresh-air line 16
downstream of the air-conditioning unit 12 and upstream of the
region of connection of the main fresh-air line 16 to the fresh-air
branch line 20. Through suitable control of the valve 26 the
electronic control unit 22 is therefore able to control the supply
of warm engine bleed air into the main fresh-air line 16. The
electronic control unit 22 is further adapted to control the
operation of the air-conditioning unit 12. Finally, the electronic
control unit 22 is used to control a heating device 28, which is
disposed in the region of connection of the main fresh-air line 16
to the fresh-air branch line 20 and is capable of purposeful and
locally selective heating of the region of connection of the main
fresh-air line 16 to the fresh-air branch line 20.
[0034] The electronic control unit 22 receives signals from
sensors, which are not represented in the figures and which measure
the static pressure in the main fresh-air line 16 and the fresh-air
branch line 20. The electronic control unit 22 is further connected
to sensors for measuring the temperature in the mixer 18 and in a
region of the aircraft that is supplied with fresh air by the
fresh-air branch line 20. If the static pressure measured by the
pressure sensors in the main fresh-air line 16 and/or the fresh-air
branch line 20 exceeds a predetermined threshold value and/or if
the temperature measured by the temperature sensors in the mixer 18
and/or in the region of the aircraft supplied with fresh air by the
fresh-air branch line 20 exhibits a predetermined characteristic,
the electronic control unit 22 evaluates this as an indication of
icing of the region of connection of the main fresh-air line 16 to
the fresh-air branch line 20.
[0035] In response to the detection of icing of the region of
connection of the main fresh-air line 16 to the fresh-air branch
line 20, the electronic control unit 22 may then execute various
control functions. One control option is to open the valve 26
disposed in the second engine bleed-air line 24 so that warm engine
bleed air is supplied to the main fresh-air line 16. As a result,
the region of connection of the main fresh-air line 16 to the
fresh-air branch line 20 is heated by the supply of warm air
through the main fresh-air line 16. In order to avoid an excessive
impairment of the cooling capacity of the aircraft air-conditioning
system 10 and hence of the comfort of the passengers and crew on
board the aircraft, these heating periods should however be kept as
short as possible. For example, the electronic control unit 22 may
close the valve 26 disposed in the second engine bleed-air line 24
again as soon as the sensors indicate a normalizing of the
pressure- and temperature values measured by them.
[0036] Alternatively or in addition thereto, the electronic control
unit 22 may start operation of the heating device 28 and hence
initiate a purposeful heating of the region of connection of the
main fresh-air line 16 to the fresh-air branch line 20. The heating
is device 28 may be for example an electric heating device. A
heating device 28 that is particularly energy-efficient to operate
is however represented in FIG. 3.
[0037] According to FIG. 3 the heating device 28 comprises a
recirculated-air line 30 for recirculating filtered cabin air of
the aircraft. In the region of connection of the main fresh-air
line 16 to the fresh-air branch line 20 the fresh-air branch line
20 extends through the recirculated-air line 30. In other words,
where necessary, warm recirculated air that is flowing through the
recirculated-air line 30 may flow around the fresh-air branch line
20. The recirculated-air line 30 opens out into the main fresh-air
line 16, so that a mixture of fresh air and recirculated air flows
through the main fresh-air line 16 downstream of the region of
connection of the main fresh-air line 16 to the fresh-air branch
line 20.
[0038] In order to enable an optimum heat transfer from the
recirculated air flowing through the recirculated-air line 30 to
the fresh-air branch line 20, the fresh-air branch line 20 in the
region, in which it extends through the recirculated-air line 30,
is uninsulated, i.e. not provided with an insulating sheath. A
purposeful heating of the fresh-air branch line 20 in the
arrangement represented in FIG. 3 is possible through control of a
valve, which is not represented and is disposed in the
recirculated-air line 30, by means of the electronic control unit
22.
[0039] Finally, the electronic control unit 22 is capable of
controlling the operation of the air-conditioning unit 12 and/or
the supply of warm air into the main fresh-air line 16 downstream
of the air-conditioning unit 12 and upstream of the region of
connection of the main fresh-air line 16 to the fresh-air branch
line 20 in such a way that the temperature of the air flowing
through the region of connection of the main fresh-air line 16 to
the fresh-air branch line 20 does not fall below a first
predetermined temperature value T.sub.1 in the range between
0.degree. C. and 5.degree. C. In this way, icing of the region of
connection of the main fresh-air line 16 to the fresh-air branch
line 20 may be reliably avoided. Such a control of the aircraft
air-conditioning system is appropriate particularly when the
cooling capacity requirement demanded of the aircraft
air-conditioning system 10 is not excessively high, for example
when the aircraft is operating on the ground at moderate ambient
temperatures.
[0040] As an alternative thereto, the control unit may control the
operation of the air-conditioning unit 12 and/or the supply of warm
air into the main fresh-air line 16 downstream of the
air-conditioning unit 12 and upstream of the region of connection
of the main fresh-air line 16 to the fresh-air branch line 20 also
in such a way that the temperature of the air flowing through the
region of connection of the main fresh-air line 16 to the fresh-air
branch line does not exceed a second predetermined temperature
value T.sub.2 in the range between -15.degree. C. and -10.degree.
C. Good dehumidification of the air may then be achieved in the
air-conditioning system 10, so that by virtue of supplying
relatively dry fresh air into the region of connection of the main
fresh-air line 16 to the fresh-air branch line 20 the risk of icing
in this region may be reduced. Such a control of the aircraft
air-conditioning system 10 is appropriate for example when the
cooling capacity requirement on board the aircraft is relatively
high and, in the event of an adjustment of the temperature of the
air flowing through the region of connection of the main fresh-air
line 16 to the fresh-air branch line 20 to a value above the first
predetermined temperature value T.sub.1, may occasionally not be
met.
[0041] FIG. 2 shows an embodiment of an aircraft air-conditioning
system 10 that differs from the arrangement represented in FIG. 1
in that the main fresh-air line in the region of connection of the
main fresh-air line 16 to the fresh-air branch line 20 branches
into a first main fresh-air line branch 32 and a second main
fresh-air line branch 34. The first main fresh-air line branch 32
and the second main fresh-air line branch 34 are each of a curved
design so that the main fresh air branch flows flowing through
these line branches 32, 34 are deflected in the region of
connection of the main fresh-air line 16 to the fresh-air branch
line 20. The fresh-air branch line 20, on the other hand, extends
once again in a direction that corresponds to the flow direction of
the fresh air flow through the main fresh-air line 16 upstream of
the region of connection of the main fresh-air line 16 to the
fresh-air branch line 20, so that the fresh air branch flow flowing
through the fresh-air branch line 20 experiences substantially no
deflection in the region of connection of the main fresh-air line
16 to the fresh-air branch line 20.
[0042] In order to reduce the risk of icing in the region of
connection of the branching main fresh-air line 16 to the fresh-air
branch line 20, the first main fresh-air line branch 32 and the
second main fresh-air line branch 34 each have a flow cross section
that is larger than the flow cross section of the fresh-air branch
line 20. Otherwise, the construction and mode of operation of the
aircraft air-conditioning system 10 shown in FIG. 2 correspond to
the construction and mode of operation of the arrangement according
to FIG. 1.
* * * * *